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rcu: Pull out wait_event*() condition into helper function 

The condition for the wait_event_interruptible_timeout() that waits
to do the next force-quiescent-state scan is a bit ornate:

	((gf = READ_ONCE(rsp->gp_flags)) &
	 RCU_GP_FLAG_FQS) ||
	(!READ_ONCE(rnp->qsmask) &&
	 !rcu_preempt_blocked_readers_cgp(rnp))

This commit therefore pulls this condition out into a helper function
and comments its component conditions.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2015-07-01 13:50:28 -07:00
parent 99a930b0d2
commit b9a425cfcb
1 changed files with 21 additions and 5 deletions
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26
kernel/rcu/tree.c
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@ -1903,6 +1903,26 @@ static int rcu_gp_init(struct rcu_state *rsp)
return 1;
}
/*
* Helper function for wait_event_interruptible_timeout() wakeup
* at force-quiescent-state time.
*/
static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp)
{
struct rcu_node *rnp = rcu_get_root(rsp);
/* Someone like call_rcu() requested a force-quiescent-state scan. */
*gfp = READ_ONCE(rsp->gp_flags);
if (*gfp & RCU_GP_FLAG_FQS)
return true;
/* The current grace period has completed. */
if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
return true;
return false;
}
/*
* Do one round of quiescent-state forcing.
*/
@ -2067,11 +2087,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
TPS("fqswait"));
rsp->gp_state = RCU_GP_WAIT_FQS;
ret = wait_event_interruptible_timeout(rsp->gp_wq,
((gf = READ_ONCE(rsp->gp_flags)) &
RCU_GP_FLAG_FQS) ||
(!READ_ONCE(rnp->qsmask) &&
!rcu_preempt_blocked_readers_cgp(rnp)),
j);
rcu_gp_fqs_check_wake(rsp, &gf), j);
rsp->gp_state = RCU_GP_DONE_FQS;
/* Locking provides needed memory barriers. */
/* If grace period done, leave loop. */